The storage and mobilization of triglycerides in adipose tissue play a central role in the regulation of glucose utilization in the body. The regulation of triglyceride storage reflects the antagonism between insulin which promotes triglyceride synthesis from glucose and catecholamines or other hormones which promote the hydrolysis of triglycerides. Many of the effects of catecholamines, including the activation of phosphorylase and triglyceride lipase, are mediated by beta-adrenergic cyclic AMP dependent protein phosphorylation. On the other hand, many of the effects on insulin, including the activation of glycogen synthetase and pyruvate dehydrogenase involve a dephosphorylation of proteins. The intracellular mediator of these and other actions of insulin has not been established. However, some evidence suggests that an increase in intracellular Ca2 ion levels may mediate some of the metabolic effects of insulin in adipose tissue. Furthermore, some of the antagonistic effects of catecholamines may be mediated by a decrease in Ca2 ion levels. However, it is not known whether insulin produces an increase in Ca2 ion levels, whether catecholamines produce a decrease in Ca2 ion levels, or how the hormones can bring about these changes in Ca2 ion distribution. More importantly, it remains unclear whether the changes in distribution are causally related to the metabolic actions of insulin and catecholamines. The proposed studies seek answers to these questions. Since changes in Ca2 ion levels can be inferred from changes in the transmembrane movements or fluxes of Ca2 ion, the effects of insulin and catecholamines on Ca2 ion influx and efflux will be determined from studies on the movement of 45Ca2 ion in isolated fat cells. Furthermore, since changes in Ca2 ion distribution may arise secondarily as a result of a primary action of hormones on the distribution of Na ion and K ion across the cell membrane, the effects of insulin and catecholamines of 24Na ion and 42K ion influx and efflux will be determined. Finally, to evaluate whether the changes in ion distribution are causally linked to changes in metabolism, studies will examine whether the changes in Ca2 ion always occur prior to the metabolic actions of insulin and catecholamines.